The present invention concerns a compensating chuck for concentrically clamping workpieces, comprising a housing, two pairs of mutually diametrically opposed main jaws for receiving corresponding clamping jaws, and a transmission for preferably radially moving the main jaws towards and away from each other.
Chucks of the above-indicated kind are also referred to as four-jaw chucks or four-jaw clamping chucks. Chucks for concentric clamping are basically required whenever workpieces have to be gripped in machine tools or for machining, which in particular are machined in a rotational mode. In modern manufacturing environments, there is an increasing need for clamping devices which can be used both for turning and also for milling. Accordingly, the invention concerns a chuck for such purposes of use. The reason for in any way considering the use of four jaw chucks in comparison with three jaw chucks is that, with a larger number of jaws which embrace the workpiece, the spot loading on each individual jaw is reduced. Consequently, with a larger number of jaws, the forces which act on the workpiece and which consequently deform the workpiece are more uniformly distributed over the periphery of the workpiece. That increases the dimensional accuracy of the workpiece after machining.
Four jaw chucks are known from the state of the art, which provide for concentric clamping. In general, however, they suffer from the disadvantage that they are only suitable for gripping round workpieces or they have to be of a mirror-image symmetrical configuration in both jaw planes so that all four jaws can engage the workpiece when gripping it. Such rigidly concentrically gripping jaws, by virtue of a lack of compensation in regard to workpiece geometry, enjoy only limited practical utility in relation to ‘non-round’ workpieces.
Four jaw compensating chucks are also known from the state of the art, which however also suffer from crucial disadvantages. In many four jaw chucks with a compensating function, the reproduction accuracy in terms of concentric workpiece gripping is limited.
WO 2011/137884 A1 discloses for example a four jaw chuck having a compensating function, such that adjacent jaws of the chuck are coupled together by way of one or more oscillating rods. When, when dealing with a workpiece which is not rotationally symmetrical, a first pair of jaws is first brought into contact with the workpiece while the other pair of jaws is not yet in contact therewith, the corresponding rods are deflected and the second pair of jaws is successively moved towards the workpiece. That kinematic structure suffers from the disadvantage that, by virtue of the lever lengths which necessarily have to be tolerated as between the drive force and the jaw, there is a certain elasticity in the system and drive force losses occur. The high level of complexity of the components involved also makes the systems potentially susceptible to fault.
A further approach for compensation in regard to four jaw chucks is to be found in the area of chucks actuable by means of power clamping. DE 10 2004 001 839 A1 discloses a four-jaw chuck in which the four jaws are pulled along conical sliding surfaces by means of a clamping cylinder. Hydraulically or mechanically implemented force directional conversion results in displacement of conical compensating elements in opposite relationship to the clamping direction, which are intended to permit jaws which are not yet in contact to approach the workpiece. This system is considered to have, in particular, the advantage that the maximum possible compensation travel is extremely short and the structural height of the clamping device overall is unacceptably high for certain purposes of use. In addition the system is again suitable for a hand clamping mode of operation.
With that background in mind, an object of the present invention is to provide a chuck which, as far as possible, alleviates the above-indicated disadvantages. In particular, the object of the invention was to provide a compensating chuck which ensures reliable centering and at the same time affords a compensation range which is as large as possible.